The documentation for PdfFileSecurity.SetPrivilege says we’re supposed to use DocumentPrivilege now instead of the PdfPrivilege enum. However, DocumentPrivilege has a serious thread safety flaw in its design. It is a reference type (i.e., a class) not a value type (i.e., a struct), so assigning one of the static fields from it DOES NOT give you a local copy. It gives you a reference to the static field’s instance, and it provides properties that let you modify the static field’s state.
DocumentPrivilege priv = DocumentPrivilege.AllowAll;
priv.AllowCopy = false;
if (!DocumentPrivilege.AllowAll.AllowCopy)
{
throw new InvalidOperationException(“Design flaw: global static data modified!”);
}
In this example, I want to change the AllowCopy property on a local instance of DocumentPrivilege, but changing its property value also changes the static instance’s value since both references point to the same instance. This makes the DocumentPrivilege class useless in a multi-threaded environment because you can’t count on any of the pre-defined fields having a known state, and the class doesn’t provide a constructor to create your own local instances.
All of the Aspose examples for DocumentPrivilege are also broken because of this design flaw. For example:
//Way2: Based on a predefined privilege and change some specifical permissions.
DocumentPrivilege privilege = DocumentPrivilege.AllowAll;
privilege.AllowPrint = false;
privilege.AllowModifyContents = false;
This “Way2” sample has just changed the global state of the AllowAll static field, which is very bad.